The lifetime of an Integrated Circuit (IC) is important in a variety of applications. In consumer products, for example, it is desirable that an IC has a minimum functional lifetime.
The aging characteristics of ICs depend upon a variety of factors. These include device fabrication attributes, environmental conditions, and operating parameters. Device fabrication attributes include aspects of the IC fabrication process that influence aging. Environmental conditions include the ambient temperature when the IC is operated, which in turn may determine the chip temperature. Functional parameters include, for example, on-chip voltages.
A conventional approach to calculating an expected lifetime of an IC is to stress test a small number of ICs in order to generate data on IC degradation and failure rates for other ICs fabricated using a similar process. As an illustrative example, a microprocessor manufacturer may use statistical techniques to calculate an expected minimum lifetime for each microprocessor fabricated from the same process. A set of microprocessors are selected as test samples. The test samples are operated at an elevated temperature to accelerate the aging process. Data on failure rates of the stress-tested microprocessors is then used to calculate the expected lifetime for other microprocessors fabricated using the same fabrication process.
The conventional approach to calculating an expected lifetime of an IC has several drawbacks. One drawback is that after initial sample data is collected, the accuracy of the estimation depends upon maintaining a constant fabrication process. However, fabrication processes may vary for different ICs. For example, some companies may use more than one fabrication facility to manufacture their ICs, and each fabrication facility may use a slightly different fabrication process. Additionally, fabrication processes may change over time, such as when processes are upgraded. As a result, process variance may degrade the accuracy of a lifetime estimate of an IC.
Another drawback of conventional approaches to calculating an expected lifetime of an IC is that the environmental conditions in which an IC is operated may vary. Since the lifetime of an IC decreases with increasing operating temperature, environmental conditions can alter the aging characteristics. In particular, the operating temperature of an IC depends upon the ambient temperature in its local environment and upon the degree to which it is cooled. For example, the use of a heat sink and aggressive cooling (e.g., a high speed fan) may reduce the operating temperature of an IC. In contrast, operating an IC with minimal cooling or in a hot environment may increase the operating temperature of the IC and hence reduce its lifetime.
Still another drawback of conventional approaches to calculating an expected lifetime of an IC is that some types of ICs have more than one possible operating state. As an example, some types of ICs have high performance and low performance operating states. These may include, for example, two or more clock rates, such as a minimum clock rate and one or more higher clock rates for higher performance. Increasing clock rates for higher performance is also known as “overclocking.” The overclocking states typically have a higher operating voltage. The higher voltage and higher heat dissipation experienced during overclocking reduces IC lifetime.
A further complication to calculating an expected lifetime of an IC is the interaction of processing variations, environmental conditions, and overclocking. For example, a particular fabrication process may cause a variation in operating temperature with respect to a baseline process. Environmental conditions add an additional variance to the operating temperature. Overclocking, which increases heat dissipation, adds still yet another variance. As a result, the cumulative variance in expected lifetime of an IC may be higher than desired.
Therefore, what is desired is an apparatus, system, and method for managing the aging of an integrated circuit.